Hawaii braced for a one-two punch from a pair of major storms barreling toward the archipelago on Thursday, with Hurricane Iselle leading the way bringing high winds and heavy surf as Hurricane Julio gathered steam behind it, U.S. officials said.

Wind shook palm trees on Hawaii's Big Island and caused white caps to form off the coast as Iselle approached on Thursday afternoon rated a Category 1 hurricane, even with the eye of the storm still about 150 miles east of the town of Hilo.

The storm, with maximum winds of 80 miles per hour, was due to make landfall on Thursday night before passing south of the state's smaller islands on Friday.

As residents and tourists alike braced for Iselle, Hurricane Julio was gaining momentum further east, and was expected to pass near Hawaii by late Saturday or early Sunday, said Ray Tanabe, acting director of the National Weather Service in the Pacific region.

The rare threat of back-to-back hurricanes sent Hawaii residents scrambling to stock up on supplies as state officials warned of the potential for flash floods, mudslides and power outages in the normally calm tourist haven.

Governor Neil Abercrombie signed an emergency proclamation, freeing up funds and resources in anticipation of the storms, and authorities advised residents to prepare seven-day disaster supply kits and cautioned them against driving except in an emergency.

"Everybody knows that a real rough time is coming," Abercrombie told a news conference.

Iselle was expected to strike the Big Island as a hurricane or tropical storm between 9 p.m. and 10 p.m. local time, bringing waves of up to 25 feet, said meteorologist Chris Brenchley of the Central Pacific Hurricane Center.

Hawaii's schools would be closed on Friday, but authorities planned to keep airports open so planes could land in an emergency, even as some airlines canceled flights, officials said.

The National Park Service said it would close its Hawai'i Volcanoes visitor center and museum. Backcountry areas and roads in the area have also been shut in the park that receives about 1.6 million tourists per year. The state's Division of Forestry and Wildlife shut its hiking trails, wildlife sanctuaries and reserves on the Big Island and Maui.

A hurricane warning was issued for the Big Island of Hawaii and its surrounding waters, according to the local National Weather Service office. A tropical storm warning is in place for the rest of the state, as well as a flash flood watch.

"Very large and damaging surf is expected to rapidly build along east- and south-facing shores today and tonight, especially on the Big Island," the central Pacific center said in an advisory. "The combination of dangerous storm surge and the tide will cause normally dry areas near the coast to be flooded by rising water."

There's a chance the volcanoes on the Big Island may weaken Iselle as it approaches, said Paul Walker, a meteorologist at AccuWeather Inc. in State College, Pennsylvania. The mountains reach 13,677 feet, according to the National Park Service. Walker said there's also a possibility Iselle will continue to lose strength and strike as a strong tropical storm, still a powerful system.

Julio may drift north and miss the islands over the weekend, according to hurricane center track forecasts. Computer models show it curving to the north and losing strength as it nears the island chain, Walker said.

Residents were stocking up on basics as authorities in Honolulu advised them to prepare seven-day disaster supply kits. Shoppers waited in lines at supermarkets with carts full of bottled water, batteries and nonperishable food.

The Pacific Tsunami Warning Center said some areas may have experienced shaking, but no tsunami was expected. The earthquake hit at a depth of 7.9 miles.

There were no reports of damage from the temblor, but the news heightened the concerns of island residents, who have been stocking up on food and water in anticipation of the approaching storms.

ELECTION PLANS

Hawaii closed all government offices Friday. Primary elections scheduled for Aug. 9 will still be held. Officials continued to prepare for Hawaii's primary election, scheduled for Saturday, but said they could reassess how to proceed on Friday after Iselle hits.

"If things are really, really bad when we make the assessment on Friday, we will consider postponing elections for whatever part of the state is adversely affected by the storm," said Rex Quidilla, spokesman for the state Office of Elections.

In Honolulu, where the sun was shining on Thursday morning, resident Don Riseborough said he was taking the weather in stride.

"Talk about the calm before the storm. It's a gorgeous day here, bright sunshine, nice trade winds, a beach day. The furniture is off the lanai, and I'm about to eat everything in the refrigerator in case the power goes out."

But on the Big Island, a downpour soaked customers who dashed from cars to the Sunshine True Value Hardware store in Kapaau, only to discover shelves already picked clean of batteries, flashlights, duct tape and plywood. But sales clerk Caryl Lindamood tried to spread a cheerful outlook.

"Mother Nature sure does like to stir things up for us, doesn't she?" she said, joking about both the incoming storms and a light 4.5 magnitude earthquake that struck the Big Island 12 miles west of Waimea on Thursday morning.

Robert Trickey, 56, an interior decorator, said he was worried about plate-glass windows that form several walls at his house near Pahoa on the Big Island, while Kailua-Kona resident Lisa Hummel, 44, said her family was filling water containers and had amassed batteries, candles and flashlights and planned to shelter in their basement when the hurricane arrives.

"We'll probably make a pot of chili and ride it out," she said.

Meanwhile, Markus Schale, general manager of Hotel Wailea on Maui, said his staff was removing all outdoor furniture from patios and around the swimming pool.

"We're delivering food and drinks to people's rooms before the storm, a sort of picnic service in the afternoon so they can stay in their rooms safely tonight," he said.